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The legal meaning of “Driving Under the Influence” (DUI)

In Illinois, “driving under the influence” (DUI) is a shortcut term for a legal offense. The phrase may work in casual conversation and in news reports. However, Illinois law defines the offense of DUI in a very specific manner.

In the American judicial system, there are several ways in which laws are made. Our elected representatives can vote to pass laws that are known as “statutes”. For example, the Illinois General Assembly www.ilga.gov voted for a statute banning smoking in public places.

Starting over 500 years ago, English judges were called upon to resolve disputes among the citizenry. Over the years, the judges laid down various rules that were designed to govern a given factual situation.

These judge-made rules are known as the “common law”. Many common law concepts migrated to the United States when the colonists arrived here. Because of the common law, you cannot build a fence on your neighbor’s property.

If the General Assembly does not like the common law, it can vote to change it. Under common law England, for instance, a tenant had almost no rights because a landowner was considered superior to a renter. Now there are many statutes that protect tenants. If your house or apartment burns down, you can stop paying rent. That was not true under the common law.

Neither a statute nor the common law, however, can make a law that is contrary to the United States Constitution. The Constitution plays a particularly significant role in protect the rights of those charged with crimes, including DUI. Thus, any law must be measured against the rights secured to you under the Fourth Amendment (no unreasonable searches or seizures).

There are over 300 million people in this country engaged in billions upon billions of interactions. No Constitution, statute or common law rule can possibly account for all the possible scenarios that are bound to arise in those circumstances. Therefore, judges are called upon to give their best estimate of how a Constitutional provision or statute had intended to address a given situation.

The DUI statute provides that “[a] person shall not drive or be in actual physical control of any vehicle within this State while under the influence of alcohol.” It does NOT require the police to prove that they 1) saw you driving 2) a truck, car or motorcycle 3) drunk.


The statute requires that you “drive” or be ‘in actual physical control“. Judges have interpreted “actual physical control” as including being asleep behind the wheel (if you awaken, you can drive off) or walking away from your vehicle (how did your car get in the middle of a cornfield if you were alone and did not drive it there) and any other indication that you either had been, or might later be, driving.

“Motor Vehicle”, by statute, includes “[e]very vehicle which is self-propelled and every vehicle which is propelled by electric power obtained from overhead trolley wires, but not operated upon rails, except for vehicles moved solely by human power, motorized wheelchairs, low-speed electric bicycles, and low-speed gas bicycles. Thus, a riding lawn mower, a four-wheeler, an ATV and a mini bike are vehicles.

“Under the influence” is not the same thing as “drunk”. You do not have to be blasted, blitzed, plastered, three sheets to the wind, bombed, falling down drunk etc. The courts have held that “under the influence” means that your ability to act and think with reasonable care is to some degree impaired as a result of alcohol.

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